1. Field of the Invention
The present invention relates to a data structure of a multimedia file format, an encrypting method and an encrypting device thereof, and a decrypting method and a decrypting device thereof. More particularly, it relates to an encrypting method and an encrypting device of moving picture files in a moving picture recorder and a reproducing device equipped with memory cards.
2. Description of the Related Art
In recent years, a morphology of contents such as moving pictures has transferred from analog data to digital data. The digitized contents can be copied without any deterioration of quality. Accordingly, content data can be copied through a CD-R, a recordable DVD disk or a memory card between users, alternatively by a file transfer technology utilizing communication network such as Internet, for example, by sending the content data attached to E mail. Such a copy operation has become rampant, which brings about problems of copyright in a content business world.
As a technique for protecting the copyright of the digital contents, there is a method for encrypting the content data. By this encryption, illegal copy can be prevented. In the conventional case of encrypting the content data, a method for sweepingly encrypting the content data in a block from head to end has generally been employed. Therefore, only those who have rights to use the data content, i.e., rights to decrypt the content data, can use the content data.
In the aforementioned conventional encrypting method, when the content data is encrypted en block from head to end, it is possible to prevent the illegal copy. However, since the content data is encrypted en block from head to end, it is not easy to access an optional position of the content data. To access the optional position, even a code of data not targeted for accessing must be decrypted. In practice, therefore, there is a problem of a useless processing requirement. That is, conventionally, accessing to the optional position of the encrypted content data requires processing for sequentially decrypting codes from the head of the content, which is carried out until a desired content position is reached. Such processing has a problem of a long processing time until data of the access position is obtained.
The processing of decrypting the codes until the desired content position is reached is necessary only for accessing a desired position, but not for actually using the content data. Thus, it can be said that it is useless processing.
As a desired access position is more apart from the head of the file, the aforementioned useless processing and the processing time are increased. Since the increases of a processing load and the processing time are accompanied by a power consumption increase, a portable equipment or the like using a battery has a problem of a reduction in continuous use time.
The accessing to the optional position of the content data is necessary for realizing, for example fast-forward reproduction, rewind reproduction, random access reproduction, and resume reproduction (function of resuming from where reproduction is stopped by a user) in reproduction of moving pictures.